This invention relates generally to a lightsafe masking film and, more specifically, to a composite, lightsafe masking film to be used for masking a portion of a photosensitive material during exposure to actinic light in the photomechanical reproduction process. The present invention is also directed to an exposure method using the above lightsafe material.
One known lightsafe masking film of this type is composed of a plastic film substrate and a peelable, lightsafe layer provided thereon. When a desired cutting line is formed on the lightsafe layer manually or with a suitable automatic cutting device and when the cut portion is removed by peeling, there leaves a desired transparent pattern (window) on the masking film. A photosensitive material is then exposed to light through the resulting masking film and a negative so that the a positive is obtained on the photosensitive material at a position corresponding to the window of the masking film.
The lightsafe layer is generally comprised of a colorant functioning as a lightsafe substance. The colorant conventionally used is predominantly a red colorant because of its good light-blocking characteristics. Lightsafe masking films with a reddish color, however, suffer from a drawback that cutting works and succeeding peeling works become inefficient since the red color of the film causes eyes of the workers to be strained and taxed. This also applies to yellow lightsafe masking films. Whilst the use of a masking film employing a green colorant could improve the workability, such a film in turn causes a problem of poor light-blocking property.
In a color photomechanical reproduction process, an original color film to be processed is first scanned with a color scanner to form a monochromatic negative for each of the four separated, cyan, magenta, yellow and black colors. When legends, illustrations, screen tints and the like modifications are to be incorporated, corresponding negatives are also prepared. These negatives are then assembled for each of the four colors. A positive film is then produced by repeated exposure of a photosensitive material, such as of a silver halide-type or a photoresin-type, through respective four assembled negatives. In this case, lightsafe masking films are used for masking desired portions of the photosensitive material.
As the masking films used in the above-described process for the production of a positive pattern, there have been used those having yellow or amber colors as mentioned previously. Since a lot of masks with different cut patterns are to be used in each exposure step, mistakes such as failure to cut and peel the masking layers have often been experienced. Further, it has been very troublesome to determine which patterns of negatives are deles (or stets).